Attach Cabinets to the van...how'd you do it? Does it work?

[grin]

I've been thinking about laying my floor down with 1/2" polyiso and then 3/8" plywood covered with linoleum.

You think the polyiso will cause rust and I should skip it? If so, what thickness of plywood should I use?

[86Scotty]

Now that's homebrew R&D!!!

[JohnandMandi]

That's what a yard is for right?

-John

[Chance]

I think most of us can agree that one of the main causes of floor rust is moisture, and if the van is used in cold weather where the metal floor will get fairly cold, moisture in the warmer air inside the van will find its way to the metal floor and condense. Once moisture condenses between the subfloor and van metal floor it's hard to get it to dry quickly before it causes damage.

In my opinion the space between the subfloor or subfloor insulation and van floor must either be left open enough to get good ventilation so it can dry quickly, or else eliminated completely so moisture can't get there at all to condense in the first place.

Where I worked in industry we always tried to insulate in such a manner that moisture couldn't get to cold surface at all. Because many of our applications were in sub-zero temperatures, moisture would freeze and the ice would grow over time causing lots of damage. If building a van for cold-weather camping I think I would insulate and seal it air tight. And in a van that can't be easy because of the floor corrugations which limit options.

[JWA]

Chance you too are spot on with your observations. I'm now on my third van where plywood only, nothing between it and the metal floor is/was the practice. With only a little bit of creative installation the air spaces under the floor can be/should be left open so natural air exchanges are made.

Trying to keep that space completely free of migrating moisture or condensation would be close to impossible. Instead of fighting nature in this case we'd be better advised to work with it.

In our cases the metal floor (under the plywood) would be slow to heat up and cool down therefore moisture inside the van above would be hard pressed to condense in that space. Since we're leaving air gaps at the front and rear of the longitudinal flooring anything finding its way in there would be able to easily escape.

Here's a few photos of my current van when it first arrived, showing the surface rust caused entirely by the OEM mat, the one I described as being thoroughly soaked through every inch of the original padding:







This is the OEM mat--it was left outside for about 5 days during a dry spell until it was fully dry:



There are several other after POR-15 treatment here: http://s184.photobucket.com/user/JWA...Ford/03%20E250 Feel free to peruse that album, ignore those photos not necessarily pertaining to this issue--its a catch all album.

So as I continue to preach the gospel of NOTHING under a plywood floor EVER in our vans I wish us all a rust free metal floor!

[Chance]

Originally Posted by JWA

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In our cases the metal floor (under the plywood) would be slow to heat up and cool down therefore moisture inside the van above would be hard pressed to condense in that space. Since we're leaving air gaps at the front and rear of the longitudinal flooring anything finding its way in there would be able to easily escape.

....cut......

So as I continue to preach the gospel of NOTHING under a plywood floor EVER in our vans I wish us all a rust free metal floor!

JWA, we are getting off topic with floor, plus I don't follow what you mean by the metal floor being slow to heat or cool down. I have no idea what time frame you are implying or how that affects condensation.

As I said in previous post, if building a new van myself I would seal it tight rather than leave it relatively open so it can breathe. Sealing the metal surface tight may be harder and more expensive but I'd prefer that option for my type of use over your recommendation. There are ways to do it right, it just takes more planning, work, and cost. But if plywood alone works for you then there is no reason for you to do more. One engineering solution is not always the best for all applications.

[JohnandMandi]

My fault for getting off topic but...

Hypothetically, if there are three coats of Por-15 on the entire floor would it eventually succumb to moisture from above or is the main concern now it rusting from below?

Secondly, is an asphalt based product enough to "seal" it properly to said thrice coated floor?

-John

[Chance]

Originally Posted by JohnandMandi

My fault for getting off topic but...

Hypothetically, if there are three coats of Por-15 on the entire floor would it eventually succumb to moisture from above or is the main concern now it rusting from below?

Secondly, is an asphalt based product enough to "seal" it properly to said thrice coated floor?

-John

John, preventing rust and preventing the migration of moisture are two different problems, although moisture can cause rust if long term. Even if the floor was made of stainless and therefore rust wasn't going to be an issue, there are reasons I personally wouldn't want condensation under the subfloor and/or the floor insulation. One of the things I hate about most older RVs is that they tend to smell musty, and that affects me big time. That's why I would want insulation installed so that moisture can't get to the cold surface to condense.

When I used the word seal it was in the context of preventing water vapor in the air inside the van from being able to find its way to the coldest surface. The metal van floor will get cold on cold days, and if the air inside the van gets humid due to occupants, the only way I know to prevent condensation is to use enough insulation to keep the inside surface above the air's dew point.

Plywood alone will serve as insulation, but depending on outside temperature and inside humidity, moisture could form on inner surface (this is unlikely). Water vapor in air can also travel between joints in plywood segments or around perimeter edges and then condense on cold metal van floor (more likely if not sealed properly).

To your second question if I understand the context properly, we often used asphalt based sealers to join sections of insulation on walls, floors, and pipe in very cold applications to prevent moisture from getting to cold surface between the different insulation sections. But the sealer is not insulation itself. Asphalt based sealers were very popular a very long time ago to seal foamglass insulation in large freezers. It was used it walls, ceilings, and particularly under concrete floors in cold rooms and freezers. With proper construction it lasted for many decades. But again, the sealer itself doesn't insulate, it just fills the gap between insulation segments to prevent moisture from penetrating through to cold surface.

[JohnandMandi]

Thanks guys. We decided to just go with plywood and carriage bolts. When we build our one cabinet we'll bolt it through both the plywood and van floor.

-John